In recent years a technique, such as OFDM (Orthogonal Frequency Division Multiplexing) or TDD (Time Division Duplex), has been used in radio communication for realizing high frequency use efficiency. A radio communication system using such a technique is, for example, 3GPP (3rd Generation Partnership Project)-LTE (Long Term Evolution).
In order to realize higher-speed communication for a next generation radio communication system, standardization of LTE-A (LTE-Advanced) is in progress in 3GPP. Carrier aggregation (hereinafter referred to as the CA) which is a technique for realizing high-speed communication by the use of a plurality of bands is known (see, for example, Japanese Laid-open Patent Publication No. 2010-178024 and Japanese Laid-open Patent Publication No. 2010-114780).
With the CA transmission and receiving are performed by the use of a component carrier group in which a plurality of (five, for example) LTE carriers (hereinafter referred to as component carriers (CCs)) are linked together.
An LTE-A user can perform LTE communication by the use of a component carrier group made up of one to five component carriers (by the use of a bandwidth of a maximum of 100 MHz, for example). Each (having a bandwidth of, for example, 20 MHz) of a plurality of component carriers used in LTE-A is compatible with LTE, so an LTE-A user can communicate with an LTE user.
Furthermore, with a TDD system the ratio of UL (Uplink) radio frames to DL (DownLink) radio frames can be controlled flexibly. With a TDD-LTE system in which TDD is applied to LTE, the ratio of UL subframes to DL subframes can also be changed. Several UL-DL subframe configurations are defined.
If a component carrier group is used for defining a UL-DL subframe configuration, a UL signal component is an interference component for a DL signal component. Therefore, only a desired DL signal component needs to be extracted on a receiver side.
On the other hand, UL signal components and DL signal components may mingle on the receiver side on the basis of a UL-DL subframe configuration in a component carrier group.
In order to extract a DL signal component without being interfered with by a UL signal component, the following method, for example, may be adopted on a receiver side. Analog filters the number (five, for example) of which corresponds to that (five, for example) of component carriers included in a component carrier group are prepared and are arranged in parallel so that they will treat the component carriers on a one-to-one basis.
A passing bandwidth of each analog filter is set according to the bandwidth of a corresponding component carrier. As a result, if a signal transmitted by the use of the component carrier group is received on the receiver side, analog filters through which the signal can pass are changed in accordance with a UL-DL subframe configuration of each component carrier at each hour. By doing so, only DL component carriers can be extracted. In this case, however, analog filters the number of which (five, for example) is the same as that of the component carriers are included. As a result, circuit scale increases.